The present invention relates in general to the forecasting of a number of products required by the market before a demand for such products is established, the ordering of materials for the products, and the manufacture of the products; and, more particularly, the invention relates to a technique associated with a method of creating a production plan that minimizes the managerial risk caused by out-of-stock and overstock conditions created by errors in forecasting the demand for a product at the time when the materials are ordered.
In a manufacturing industry where speculative productions are performed, the number of ordered products is forecasted before an order for the product is established. Then, the materials are ordered. Generally, a long time of more than one month is required to procure the materials. Therefore, the amount forecasted at the time when the materials are ordered may be different from the actual demand. Where the actual demand is smaller than the amount forecasted at the time when the materials are ordered, an excess stock is produced. In the reverse case, an out-of-stock condition will occur. Such conditions may lead to a loss in profit. Furthermore, the out-of-stock condition will incur a decrease in the amount of sales, putting pressure on the corporate management. Therefore, it is desired that overstock and out-of-stock conditions be prevented as much as possible.
To prevent the occurrence of overstock and out-of-stock conditions, the date at which products are introduced and the amount (hereinafter referred to as the introduction plan) have been heretofore predetermined at the time when the demand is established. When the introduction plan is created, the amount of materials is adjusted to compensate for oversupply or undersupply caused by a difference between the amount forecasted at the time when the materials are ordered and the actual demand. In addition, it is necessary to determine the amount of introduction, such that the production is produced within the operation time of the production line. That is, each one of many kinds (more than hundreds of kinds in some cases) of products must be judged to determine whether its parts are sufficiently or insufficiently available. The excess parts must be assigned to insufficient parts of other products. Then, the date of introduction and the amount of introduction must be determined such that the operating time of the production line is not exceeded and that the products are delivered at the date of request. Especially, where the amount forecasted at the time when the materials are ordered is greatly different from the actual demand, the amount of adjustment is large. The introduction plan is created involving many process steps. Furthermore, in some cases, it is impossible to fully compensate for an oversupply or an undersupply of materials or to adjust the load on the production line in spite of the fact that the introduction plan has been created with many process steps. As a result, an overstock or out-of-stock condition is produced.
As a technique for coping with such demand variations, JP-A-11-96210 discloses a technique for adjusting for an overload by calculating a planned load on the equipment from the number of products planned to be fabricated and reducing a load exceeding the processing capability of the equipment in accordance with a specified reduction policy. Also, JP-A-9-277142 discloses a technique for adjusting for an oversupply or undersupply of ordered materials, by forecasting the ratio of optional products producing violent demand variations or long lead time products relative to the group of products. Another, generally used method of eliminating a shortage of materials is disclosed by Kazunari TANAKA in Illustrated Inventory Control, Nippon Jitsugyo Publishing Co., Ltd., 2000. In particular, when materials are ordered, it is assumed that a certain amount of shortage will occur. The amounts of materials exceeding the required amounts are ordered as safety inventory control.
However, with the techniques disclosed in the above-cited JP-A-11-96210 and JP-A-9-277142, it is only possible to adjust one of oversupply or undersupply of materials or an excess of production capacity produced by demand variations. It has been impossible to adjust both at the same time.
Furthermore, in the technique described by Kazunari TANAKA in Illustrated Inventory Control, Nippon Jitsugyo Publishing Co., Ltd., 2000, a safety stock quantity is determined based on the assumption that the transition of a variation of a forthcoming amount of a request is similar to the transition of a variation of the past sales achievements. Therefore, when the transition of a variation of a forthcoming amount of a request is greatly different from the transition of a variation of the past sales achievements, as typically occurs in the initial or last stage of a product life cycle, an appropriate safe stock quantity cannot be set. This results in an overstock or out-of-stock condition.